Internal combustion engines generate exhaust gases in a series of positive pressure pulses. Between each positive pressure pulse, negative pressure conditions are created which result in exhaust gas reversal through the exhaust system. If the back flow reaches the internal combustion engine, the performance thereof will be adversely affected. In particular, reversionary gases can enter the cylinders of the engine upon opening of the intake valves. This will result in a lowering of torque and peak horse power as well as in a fall off of the fuel economy of the engine.
A number of anti-reversionary devices have been devised for dealing with this problem. Typically, anti-reversion devices comprise baffles or barriers inserted in headers or exhaust pipes which create turbulence in the exhaust gases to impede back flow. Such devices are not effective over a full range of engine speeds. Furthermore, such devices can be relatively expensive, not only with regard to their construction but installation thereof as well.